A gas that behaves as randomly moving, non-interacting molecules. This allows a simplified equation of state.

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Mass of air inside air balloon

I have an exercise here with a solution. The basic outline of the problem is: Calculate the mass of air inside a hot air balloon, given the mass of the air balloon at rest is $m_b = ...
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1answer
19 views

Thermal expansion coefficient times temperature: under which condition is it unity?

In Landau's Fluid Mechanics p. 8 (2nd edition) he writes for the thermal expansion coefficient $\beta = (1/V) (\partial V/\partial T)_P$: For a column of gas in equilibrium which can be taken as a ...
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2answers
36 views

Not Quasi-static, yet reversible process? Is this a valid example?

Imagine a gas (at room temp. and pressure) enclosed in a thermally insulating spherical container. At some instant, the container instantly expands symmetrically (radially outward) to, say, twenty ...
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0answers
20 views

Examples of nearly perfect fluids and gases

When learning for physics (hydrodynamics and gases) I wanted to know what would be examples of nearly perfect fluids (no surface effects and no friction) and perfect gases (only elastic collisions and ...
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2answers
244 views

Calculating Air Density Lapse With Altitude (Specifically, pressures)

This might be a bit more of an engineering question, but I'm calculating air density drop-off with altitude, and I'm having some problems calculating the pressure (I'll run through my method). This ...
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1answer
54 views

Euler Equations, Sod shock tube & conservation

Conservation of momentum? I am considering the Euler equations in conservative form and solving the Sod shock tube problem I have written a Godunov finite volume type solver. It solves for density ρ, ...
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4answers
1k views

Deriving combined gas law from Boyle's and Charles' laws

I know that the combined gas law, $$\frac{PV}{T}=k$$ should be derivable from Boyle's Law and Charles' Law. Since these are very basic equations, I presumed that it would be a simple matter, so I ...
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1answer
40 views

Is there a name for a substance that is a gas at room temperature?

Is there a name for a substance that is a gas at room temperature, such as Hydrogen, Helium, Neon, Argon, Krypton, Xenon, Chlorine, Fluorine, Bromine, Nitrogen, and Oxygen. I am writing a paper where ...
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69 views

Are Mach Diamonds radially symmetrical?

Videos like this show a form that suggests a radial symmetry in the gas jet. The same is reinforced by schematic illustrations. But other images, like this, look like there is a twisting structure ...
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242 views

Conversion of ideal gas to real gas via $Z$ compression factor

The ideal gas equation $PV=nRT$ can be converted into real gas equation by compression factor $Z$ i.e $PV=Z~ nRT)$. My question is what is $Z$ and how does it arise? Is $PV/nRT$ a compression ratio of ...
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2answers
58 views

Can we apply $pV^\gamma$=const only for quasistatic adiabatic process?

But If this is so, I have often seen people applying this formula for quick processes where no heat exchange is possible. Here is an example from where I am quoting the following: we will assume ...
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1answer
17 views

Perfect Ideal Gas Modelization of Air

I'm solving a Thermodynamic problem. I have Air at temperature of 293.15 K, and pressure of 20 MPa. I would understand if is possible to consider this an Ideal Gas or not (and if is possible which are ...
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0answers
22 views

Calculating the volume of carbon dioxide released to the atmosphere [closed]

I've heard that 6 billion tons of carbon dioxide is released to the atmosphere by humans. So I wanted to calculate the volume just for the interest. Please check my working. Molar mass of CO2 = ...
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1answer
34 views

Excluded Volume Calculation in Van der Waals Equation

When accounting for the excluded volume for in the Van der Waals equation, it is assumed that the molecules are hard spheres and are of diameter. If we consider a cube of volume V, then we can say ...
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0answers
13 views

Effusion of particles from one box to another - pressure calculation

Suppose we have a container divided into equal halves. Right half is fixed at temperature $T$, volume $\frac{V}{2}$. Initially it has pressure $P_0$, a hole of area $A$ is opened between them. I ...
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1answer
43 views

Stagnant Air Deep Inside Vintage Mines

This is really a question more about mining ventilation than true "physics." I occasionally explore a southwest desert mine, but am aware of the hazards - typically passing over half a dozen vintage ...
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2answers
67 views

Temperature of ideal gas after volume increases in piston

A three part question, all related Part 1. My question is about an ideal gas in a rigid container with two (equal volume) compartments separated by a rigid wall. One compartment has an ideal gas at ...
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2answers
40 views

Question about Charles' law:

Charles's law says that the volume of a given mass of a gas is directly proportional to its absolute temperature. This means if we increase one, the other one is automatically increased. So the ...
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2answers
63 views

Classical and Semi-classical treatments of the ideal gas

In the semi-classical treatment of the ideal gas, we write the partition function for the system as $$Z = \frac{Z(1)^N}{N!}$$ where $Z(1)$ is the single particle partition function and $N$ is the ...
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1answer
57 views

Quick question on ideal gas law

I know that the ideal gas law is: $$P = nkT$$ So Pressure = Number of Particles per unit volume * kT Why is the number of particles per unit volume = $\frac{\rho}{\mu M_H}$? Shouldn't it simply ...
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1answer
41 views

Entropy and chemical potential of an ideal gas

I am reading Schroeder's book "Thermal Physics". One calculation in the text was not quite clear to me. The entropy of an ideal gas is given by the Sackur-Tetrode equation: $$ ...
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2answers
620 views

How do you calculate the change in temperature of an adiabatic system?

I really don't even know how to start doing this problem. I understand PV=nRT and I understand that if either T, V, or P is kept constant, then the other 2 change at the same rate, and I understand ...
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2answers
80 views

Why is a material such as plastic air-tight?

I'm not too familiar with fluid mechanics, but i always wondered how let's say plastic containers would be able to contain a fluid, such as gas or water. How does plastic prevent the molecules of the ...
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1answer
27 views

Kinetic energy of a gas molecule

I am working through the derivation of the equation $$pV=\frac13mNC_{rms}^2,$$ but relating to this formula my textbook states that the kinetic energy of an average molecule of gas is given by ...
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1answer
287 views

Understanding Charles's Law

Charles's law states that, The volume of a given mass of an ideal gas is directly proportional to its temperature on the absolute temperature scale (in Kelvin) if pressure and the amount of gas ...
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1answer
58 views

Physical properties of cigarette smoke

I've been trying to find papers that list various properties of idealized cigarette smoke( ex. the molar mass, gas compressibility factor, density of smoke exiting a cigarette) but I have had very ...
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48 views

If air was significantly compressed, and then the force compressing it suddenly disappeared (no container), what would happen?

Question: If air was significantly compressed, and then the force compressing it suddenly disappeared (no container), what would happen? Side Question: I'm imagining significantly compressed, but ...
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2answers
3k views

In an ideal gas, if temperature increases, will pressure or volume increase?

This question came up when I was talking about the atmosphere. Someone had mistakenly claimed that as temperature increases, the density of the atmosphere should increase as well. I reasoned from the ...
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2answers
33 views

Temperature in an isobaric process

I have a certain conceptual issue - I'm solving heat engine problems and I found something difficult to understand. Let's take an isobaric part of a cycle of an engine, let's say that the ideal gas is ...
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1answer
48 views

Do gases have a general upper limit of density?

Is there some limit for the density of gases, at which no change in condition could make it more dense without making it fluid, or solid - or something 'in between'?
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3answers
133 views

How to calculate new air pressure with temperature change? [closed]

The question: The gauge pressure in your car tires is $2.60 * 10^5 N/m^2$ at a temperature of $35.0°C$ when you drive it onto a ferryboat to Alaska. What is the gauge pressure later, when the ...
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1answer
79 views

What volume of helium at standard ambient pressure and temperature is required to lift one kilogram of mass? [closed]

I used the Ideal Gas Law PV = nRT where P is the pressure of the gas P = 1.033 kgf/cm squared V is the unknown volume of the gas n is the amount of substance of ...
3
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1answer
135 views

How do you explain the fact that when air expands freely into an evacuated chamber from a constant pressure atmosphere, its temperature increases?

I came across this paper: Baker, B. (1999). An easy to perform but often counterintuitive demonstration of gas expansion. American Journal of Physics, 67(8), 712-713. ...
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1answer
112 views

Doubts about the ideal gas law

EDITED AND SOLUTION: In fact my stupid mistake was to take the wrong value for my $P_1$ and I was getting an 1.2998 that finally is a 1,9178 within just a difference about 7%. So at the end they are ...
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1answer
137 views

Understanding collision terms in Boltzmann equation

I am reading a paper that deals with the Boltzmann equation. They add a collision which is supposed to account for collisions which happen when particles are within a radius of $d$ from each other. ...
2
votes
1answer
58 views

Is there a standard reference where entropy is set equal to zero in property tables?

For practical considerations, it seems that entropy is only meaningful as a difference between states, like $\Delta s$ going from state A to state B. For an ideal gas, for instance, standard formulas ...
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2answers
71 views

Work done by isothermal expansion from two different viewpoints

Consider an adiabatic system as follows. It consists of a gas in a container and a piston. Initially, the system is at equilibrium and the gas inside it occupies a volume $V_i$ at a pressure $p_i$ ...
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3answers
195 views

Physical intuition for independence of components of velocity in derivation of Maxwell–Boltzmann distribution

Maxwell derived the shape of the probability distribution of velocity of gas particles by starting with just two assumptions. These are: The probability distribution is rotation invariant. The ...
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2answers
8k views

Why does a gas get hot when suddenly compressed? What is happening at the molecular level?

My guess is that the molecules of gas all have the same speed as before, but now there are much more collisions per unit area onto the thermometer, thus making the thermometer read a higher ...
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2answers
33 views

Infinite heat from gas?

Does any type of gas keep the same temperature if is constantly exposed to same force? In other words, must we change the applied force in some moment to get heat again, or is the same constant force ...
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1answer
68 views

How do we know that the Virial Expansion exists?

How do we know that the Virial Expansion exists? How do we know that we may always write $\frac{p}{kT}$ as a power series in $\frac{N}{V}$? That is, how do we know that there exists $B_{i}$ so that ...
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1answer
337 views

Enthalpy Change in Reversible, Isothermal Expansion of Ideal Gas

For the reversible isothermal expansion of an ideal gas: $$ (1)\ {∆H}={∆U}=0 $$ This is obvious for the case of internal energy because $$ (2)\ {∆U} = \frac {3}{2} n R {∆T} = 0 $$ and $$ (3)\ {∆U} = ...
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5answers
437 views

Does it take infinite energy to create a perfect vacuum?

Question is inspired by a recent burst of perpetuum mobile-type questions. It would be nice if one could simply discard them all by an argument that shows it's impossible to create a perfect vacuum. ...
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1answer
235 views

Is temperature-induced change in the volume of balloons dependent on gas?

Which balloon will have higher relative change in volume, helium balloon immersed in liquid nitrogen or air balloon immersed in liquid nitrogen? Since volume is directly proportional to temperature ...
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1answer
363 views

Velocity of real gas molecules?

It is known that the velocity of ideal gas molecules can be computed using Maxwell-Boltzmann law of distribution of molecular velocities, with average velocity given as: ...
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1answer
317 views

Compressed air in a volume: Can I determine its temperature?

Using a compressor, I augment the pressure in a volume (using atmospheric air). I only measure the pressure inside. I now that the density will increase however, the temperature decreases. Can any one ...
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1answer
188 views

Do ideal gases at zero Kelvin have potential energy?

Do ideal gases at zero Kelvin have potential energy?
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1answer
38 views

Expansion of ideal gas

Consider an ideal gas in a chamber (A), separated from another chamber (B) by a diaphragm, in the following two situations: (1) Instantaneously burst the diaphragm (2) Plug in an isentropic nozzle so ...
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2answers
2k views

Root Mean Square Speed of Gas

The RMS speed of particles in a gas is $v_{rms} = \sqrt{\frac{3RT}{M}}$ where $M$ = molar mass; according to this Wiki entry: http://en.wikipedia.org/wiki/Root-mean-square_speed The gas laws ...
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124 views

Ideal gas law problems

I got really confused about real gases volume and ideal gas volume. Ideal gas molecules take up no space, if we put gas into a 2.4L water bottle, we know that all the gas will expand all over the ...